No heat source. It's definitely a scrape of some kind. The weird part is that there are no other 'scrapes' on any other of the underside plastic pieces so I'm stumped. And I can't blame this on the dealer either, at least not from Thursday's service. I watched the footage from my dash cam and there were no incidents of anyone running up against a curb. So this will just have to remain a mystery for now but I'll definitely keep an eye out for anything that may have caused this. Thanks to all for their input.

I lost a protective panel from the underside when driving over a snow berm left by the plow. It was held in by a couple plastic fasteners. Another panel was left dangling by one fastener (the panel inside the driver's side wheel well).